The COVID-19 pandemic inspired many scientists to analyze patient blood samples to better understand SARS-CoV-2 infection and the host immune response against this novel pathogen. Cytokines are particularly informative because they act as protein messengers and affect cellular functions such as inflammation. Furthermore, tracking cytokine levels over the course of an infection or analyzing them in the context of variable COVID-19 disease severities is necessary to guide diagnosis and treatment. However, plasma cytokine levels fluctuate, and they are often low in healthy controls, so researchers need to employ especially sensitive assays.

To gain the sensitivity and reproducibility that they need, scientists researching COVID-19 turned to Simple Plex™ assays run on the Ella™ instrument to detect cytokines in patient blood samples. These automated immunoassays simply require researchers to pipette their diluted samples and wash buffer into a microfluidic cartridge, press “start” in the software program connected to the Ella machine, and walk away. Simple Plex cartridges are preloaded with analyte-specific capture and detection antibodies. Depending on the cartridge type, samples are tested in duplicate or triplicate, and up to eight proteins can be detected simultaneously from a single sample aliquot in about an hour.

Researchers can choose from a number of premade multiplex cartridges, or they can design their own custom panel. Simple Plex assays measure cytokines and other proteins in human and mouse samples from serum, plasma, and supernatant. The assays have a dynamic range that is 1-2 logs greater than standard ELISAs, enabling researchers to detect cytokines in the fg/mL to low pg/mL range.1,2 Results from studies using Simple Plex with Ella have proven to be reproducible between researchers at independent laboratory sites.2

Scientists studying COVID-19 with Simple Plex assays discovered evidence of a dysregulated antiviral immune response in blood samples from patients with severe symptoms. These aberrant responses involve an increase in pro-inflammatory cytokines, often referred to as cytokine release syndrome, that triggers local and systemic inflammation.3,4,5 Some of these cytokines induce the expansion of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs), which inhibit T cell responses against SARS-CoV-2.Using a Simple Plex cartridge that tests a panel of cytokines, researchers found a correlation between PMN-MDSCs and cytokine levels in blood samples from patients with severe disease.Another research group studied Multiple Inflammatory Syndrome in Children (MIS-C)—a delayed and severe complication of SARS-CoV-2 infection that affects seemingly healthy children. MIS-C has clinical features of Kawasaki disease (KD) and Toxic Shock Syndrome (TSS), so scientists compared cytokine levels in patient samples from all three disorders along with other forms of COVID-19. With the Simple Plex immunoassays, the researchers found unique signatures of MIS-C compared to these other conditions, along with some similarities in pro-inflammatory cytokines compared to TSS and KD.7

Using Simple Plex assays on the Ella system, researchers have made large strides in understanding a novel pathogen. In COVID-19 and many other infectious diseases, discovering which cytokines are elevated throughout disease progression and learning how they correlate with patient outcomes could lead to new treatments to reduce disease severity and death. 


  1. R. Ter Horst et al., “Host and environmental factors influencing individual human cytokine responses,” Cell, 167:1111-24.e13, 2016.
  2. P. Aldo et al., “Simple Plex™: A novel multi-analyte, automated microfluidic immunoassay platform for the detection of human and mouse cytokines and chemokines,” Am J Reprod Immunol, 75:678-93, 2016.
  3. S. Dayarathna et al., “Similarities and differences between the ‘cytokine storms’ in acute dengue and COVID-19,” Sci Rep, 10:19839, 2020.
  4. V. Bordoni et al., “The unbalanced p53/SIRT1 axis may impact lymphocyte homeostasis in COVID-19 patients,” Int J Infect Dis, 105:49-53, 2021.
  5. C. Marchetti et al., “Targeting of the NLRP3 inflammasome for early COVID-19,” biorxiv, 2021.
  6. A. Sacchi et al., “Early expansion of myeloid-derived suppressor cells inhibits SARS-CoV-2 specific T-cell response and may predict fatal COVID-19 outcome,” Cell Death Dis, 11:1-9, 2020.
  7. M. Moreews et al., “Polyclonal expansion of TCR Vbeta 21.3+ CD4+ and CD8+ T cells is a hallmark of Multisystem Inflammatory Syndrome in Children,” Sci Immunol, 6:eabh1516, 2021.